This invention relates to gel compositions and to a method of forming an organosilicon gel with a gelling agent which is a certain cholesteryl and cholestanyl ester of anthracene analogues and derivatives thereof.
A gel is a semisolid system having a high viscosity in the form of a jelly or paste. It is a two phase colloidal system consisting of a solid and a liquid in more solid form than a sol. It is believed that the initial step in forming a gel from an emulsoid begins with a fluid sol which includes concentrated droplets of disperse phase scattered throughout a dilute solution of a dispersion medium. Upon cooling the sol there is a disturbance of the equilibrium between the droplets and the surrounding dilute solution. The droplets draw the dilute solution into themselves, increase in size, and come into contact with one another forming cells like a honeycomb. This change results in a substantial decrease in fluidity which progresses to a sponge like structure representing a semi-solid jelly otherwise known as a gel. Continuation of the process results in the viscous particles uniting to form a continuous phase which encloses the droplets of what was previously the dispersion medium. The structure of the original emulsoid is thereby completely reversed with the more concentrated phase functioning as the dispersion medium while the more dilute phase is discontinuous.
A gel has also been defined as a crosslinked polymer network which is swollen in a liquid medium. The liquid prevents the polymer network from collapsing into a compact mass and the network in turn retains the liquid. The most familiar gel is the dessert JELLO.RTM., a trademark of the General Foods Corporation, White Pains, N.Y., in which the network constitutes polymers derived from animal protein gelatin whereas the liquid is colored flavored sweetened water. While some gels are crosslinked chemically by covalent bonds other gels are crosslinked physically by weaker forces such as hydrogen bonds and van der Waals forces. JELLO.RTM. is a physically crosslinked gel which can be reversibly dissolved by moderate heating.
In U.S. Pat. No. 4,790,961 issued Dec. 13, 1988 there is described a thermally reversible gel and a method for the formation of gels of certain organic liquids by adding to the organic liquid a gelling agent which is a cholesteryl and cholestanyl ester of anthracene and anthraquinone analogues and derivatives thereof. The mixture is heated until homogeneous and upon cooling a gel is said to form. Exemplary of the organic liquids that are said to be capable of being gelled in accordance with the '961 patent are n-dodecane a saturated aliphatic hydrocarbon, and 4-heptanol and n-octanol which are aliphatic alcohols. While the disclosure of the '961 patent is primarily directed to the formation of gels of such organic liquids, the '961 patent does mention "silicone oils". However, in attempts to follow the teaching of the '961 patent it was found that gels of organosilicon compounds could not be formed in accordance with the teaching of the '961 patent. It was discovered that organosilicon gels could be formed nevertheless by a new and novel procedure which is beyond the scope of the '961 patent and which new and novel procedure constitutes the method of the present invention for the production of unique gels. In addition it was discovered that contrary to the teaching of the '961 patent that the gels which were formed were thermally irreversible rather than thermally reversible as specified in the '961 patent. Thus upon melting the gels of the present invention collapse to a cloudy white mixture which is transformed to a clear liquid containing suspended crystals of the gelling agent. Such new compositions are not taught in the '961 patent nor contemplated therein.
The gels of the present invention are further distinct from the gels of the '961 patent in that the instant gels are stable at temperatures much in excess of their initial temperature of gelation. Some gels produced in accordance with the present invention have been found to gel at temperatures above room or ambient temperature. Since the gels of the '961 patent are thermally reversible such gels are destroyed at temperatures in excess of 50-70 degrees Centigrade whereas the gels disclosed herein are stable at elevated temperatures in excess of one hundred degrees Centigrade.
Gelled antiperspirant formulations are not new as evidenced by U.S. Pat. No. 4,954,333 issued Sep. 4, 1990 in which dibenzylidene sorbitol is included as a gellant in a composition containing a silane. Novel gelled antiperspirant products however may be produced in accordance with the present invention by employing the gelators of the '961 patent in combination with certain siloxanes. It is also significant to note that unexpectedly the presence of solid particulate matter such as the antiperspirant active ingredient or the clay additive does not destroy the formation of the gel and has not been found to cause any disruption in the gel network.